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March 29th, 2011, 04:46 PM  #1 
Senior Member Joined: Mar 2011 Posts: 105 Thanks: 0  Probability, help me, please, So confusing
The problem is Find the probability when have at least 2 heads in 3 tosses of a coin I can solve it by the list. But is's too slow if I have a big number Like, The probability when have at least 3 heads in 5 tosses Somebody solve it, by use combination like 5C3/(1/2)^5 But I'm so confused, the we use conbination if the position of heads and tails are not important. But here, the position is important. Why everybody solve it by using the combination 
March 29th, 2011, 04:53 PM  #2 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 520 Math Focus: Calculus/ODEs  Re: Probability, help me, please, So confusing
See this topic for my "explanation" of the use of combinations for this type of problem: http://www.mymathforum.com/viewtopic.php?f=24&t=19861 

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